X-ray powder diffractometry is used to determine the identity of substances as well as for other types of analyses. In essence, a small collimated beam of nearly monochromatic X-rays is directed onto a polycrystalline specimen in the form of powder, producing a diffraction pattern that is recorded on film or with a counter tube. This X-ray pattern is a uniquely characteristic property resulting from the atomic arrangement of the diffracting substance. Different substances have different atomic arrangements or crystal structures; hence, no two chemically distinct substances give identical diffraction patterns.
It is generally the practice for technicians conducting routine X-ray analyses to change each sample by hand. When a large number of samples are being analyzed, such manual manipulations are time-consuming, troublesome and costly. Consequently, there is a need for an automatic sample changer which can make unattended analyses of multiple samples.
U.S. Pat. Nos. 3,527,942 to Roe, et al. and 3,920,151 to Roe each disclose an automatic sample changer in which samples are configured into a cylindrical or plate-like pellet and aligned on edge in an inclined loading ramp which gravity feeds the pellets sequentially to a sample holder. The pellets roll one at a time into a channel in the sample holder for analysis. However, the ability to automatically and efficiently change samples in powder form is not heretofore known.